In descriptive statistics, the quartiles of a set of data values are the three points that divide the data set into four equal groups, each group comprising a quarter of the data. The first quartile (often called Q1) is defined as the number halfway between the smallest number and the median of the data set. The second quartile (Q2) is the median of the data. The third quartile (Q3) is the middle value between the median and the highest value of the data set.